This invention relates to an improvement in a piezoelectric tuning fork vibrator used as an oscillator or a detection element in various electronic circuits, and more particularly to a piezoelectric tuning fork vibrator of high accuracy and free from characteristic variation.
Conventionally, the piezoelectric tuning fork vibrator, as shown in FIG. 1, has a fundamental construction, in which a vibrator body 11 of an elasticity invariable material, such as elinvar, is provided with a slit 12 extending from one end to an intermediate portion of body 11 to form opposite tuning fork legs 13 and 14 at both sides thereof, one leg 13 being provided at the outside surface with a piezoelectric thin film 15, such as ZnO, and an electrode 16 on the film 15.
The piezoelectric tuning fork vibrator, as shown in FIG. 2, is supported by pin terminals 17 and 18 each welded at one end to one face of vibrator body 11 and embedded at the other end in a support member 19. The pin terminal 17 perforates the support member 19 and projects downwardly therefrom so as to be one electrical lead terminal and the electrode 16 is connected through a lead wire 20 to a terminal 21 perforating the support member 19 so as to be the other lead terminal.
In such a piezoelectric tuning fork vibrator, the tuning fork legs 13 and 14, when different in width, differ in the resonant frequency so as to cause omission of vibration (sound leakage) at the portion which supports the tuning fork vibrator.
The occurrence of omission of vibration makes the characteristics of the device unstable so that the resonant frequency varies due to the manner of support of the vibrator and the voltage build-up rate lowers, and as a result the vibrator is not suitable for an oscillator of high accuracy.
FIG. 3 shows the relation between a difference in width of the legs and the resonant frequency variation, in which the abscissa represents a difference .DELTA..omega. in leg width and the ordinate represents the relative change in the resonant frequency.
The resonant frequency variation shown in FIG. 3, is the difference obtained by subtracting the resonant frequency of the piezoelectric tuning fork vibrator in a freely hanging condition B from that of the vibrator in a stationary condition A is divided by the latter resonant frequency.
Thus, it can be seen that the existence of a difference in width of the leg will cause the resonant frequency to vary approximately in proportion to the difference.
The conventional piezoelectric tuning fork vibrator has been machined to form both tuning fork legs 13 and 14 themselves equal in width before providing one leg 13 with the piezoelectric thin film 15 and electrode 16.
However, the legs 13 and 14, even if equal in width, become unbalanced to the extent of adding the piezoelectric thin film 15 and electrode 16, thereby creating the problem that a resonant frequency difference develops so as to cause the omission of vibration.
An object of the invention is to provide a piezoelectric tuning fork vibrator whose tuning fork legs to not differ in resonant frequency, is free from the omission of vibration, and has a high accuracy.
Another object of the invention is to provide a piezoelectric tuning fork vibrator which is capable of obtaining a high accuracy without using particular processing.